4. observe that TX led blinks on UNO, serial monitor shows data coming across (although its gibberish) a. In addition, using usblyzer, Bulk data transfers are logged. 5. disconnect USB cable from UNO6. connect Roland UM1 USB/MIDI cable to PC and to MIDI OUT of Olimex MIDI shield.7. connect 9v power supply to UNO8. Observe that TX led no longer lights up a. although if I code the LEDs on the Olimex to light during main loop, they do indeed light.9. Using MIDI OX, selecting UM1 as the MIDI source, no MIDI data transmitted. Close MIDI OX10. Using USBlyzer, select UM1 USB device, No data comes over the wire.11. Volt meter shows 5v on MIDI OUT pins 4,5.12. 5v on THRU pins, 4,5.

The conclusion that I've reached is that the UNO, by itself, is transferring data across a standard usb cable to the PC/SerialMonitor/USBlyzer (or other port monitor app). But when the MIDI shield is attached and the standard USB cable is not connected, no serial data is being sent.

The question remains, how can I verify that serial data (MIDI data) is being send from the TX pin, out the MIDI OUT and across the wire? I haven't ruled out that it's a mA issue, but that seems unlikely since others have reported the mA under load is about 2,5mA. I'm not sure how to measure the mA using a standard multimeter, but I would doubt that I'd be able to detect it.

update: I picked up some 5v 20mA LEDs and inserted into pin 4 &2 of the MIDI OUT DIN, ran a sketch and the LED blinks. However I'm unable to read any mA's. That could be my meter. I am able to see the voltage drop using my meter. So it would appear something going out the MIDI OUT DIN?

It has to be 5mA to work. If I slow down the baud rate enough, would I be able to detect if it's hitting 5mA to 0mA?

And for those still reading this saga: check out oxmidi project. could be useful.

Olimex finally contacted me and they weren't much help unfortunately. They test these boards by connecting them to each other and sending MIDI back & forth. I don't believe they even test these on MIDI devices! grrr

Not sure what you mean by the 'rest state', but the '0' or 'off' signal is 5mA (which is not 'off' at all, but that is the way the hardware standard is defined), sort of inverse logic. I am sure there are good electrical/comms reasons to define it that way, but I don't know whatthey are.